This disclosure relates to signal processing. More particularly, the present disclosure related to a system and method for distortion limiting.
In an audio system, when the amplitude of an audio signal exceeds the maximum voltage capability of the system the output signal stops abruptly at the voltage limit causing the tops and bottoms of the audio wave form to be, in effect, cut-off, resulting in clipping. To a worse extent, in the frequency range that is below the resonant frequency of a loudspeaker, for example a woofer, substantial distortion could be produced even when the speaker is driven by a voltage well below the maximum level. To address these problems, limiters are often used to limit the output voltage to speakers at high output levels.
A conventional limiter is a single band configuration that applies a limiting gain to all frequencies equally. Since music is generally a dynamic and broadband signal, such a configuration may cast unfavorable performance limitations to an audio system. For example, one prominent drawback with the conventional limiter is that there is often a compromise between bandwidth and maximum output sound level. More specifically, if the system engineer prefers louder sound for a speaker at maximum output, which is typically true, he/she would have to reduce the operation bandwidth of that speaker in order to meet the distortion performance threshold, as illustrated by line 102 of FIG. 1A. The bandwidth cut back is typically done by increasing the cut off frequency of the high pass filter in the system equalizations, which will effectively remove much of the bass content. As a result, a substantial amount of bass capability of the speaker cannot be utilized. On the other hand, if the system engineer prefers to retain the deeper bass frequencies, he/she would have to tune the limiter in a very aggressive way to lower the sound level at maximum output in order to meet the distortion performance requirement, as illustrated by line 104 of FIG. 1A.